1. Field of the Invention
The present invention relates to a circuit, and more particularly to an impedance matching circuit and method.
2. Description of the Related Art
The speed of transmission is critical in digital data transmission. Therefore, the output impedance of the driver must match with the impedances of the external transmission line to reduce occurrence of signal distortion in digital data transmission in hardware of personal computer, such as display cards and memory device, or that in external transmitting devices, such as USB, RS 232 and IEEE.
In the prior art semiconductor circuit design, the materials serving for output impedance are usually made of polysilicon, diffused or well resistors and an external serial resistor. The resistance of the semiconductor resistors, however, are unstable and have ±30% accuracy variation roughly. As a result, the output impedance of the final circuit is usually different from what was desired. Therefore, the external serial resistor usually needs to be adjusted in order to compensate the variation of the semiconductor resistance so that the overall output impedance can fit requirement but after all, the variation of the output impedance always exists.